caa a22 4500 378913670 CHVBK 20180305123548.0 cr unu---uuuuu 161128e20040401xx s 000 0 eng 10.1524/zpch.218.4.457.29195 doi (NATIONALLICENCE)gruyter-10.1524/zpch.218.4.457.29195 Troe Jürgen Limitations of Variational Transition State Theory for Barrierless Radical-Radical Recombination Reactions [Elektronische Daten] [Jürgen Troe] Variational transition state theory (VTST) is widely used for the modelling of barrierless radical–radical recombination reactions. In this application, VTST suffers from a number of limitations some of which are of more technical, others of more fundamental nature. The former are caused by inappropriate averaging over individual adiabatic channel potentials or by the neglect of quantum effects, the latter are due to deviations from adiabatic dynamics. It is shown that most radical–radical recombination reactions are characterized by Massey parameters which are smaller than unity such that the dynamics is nonadiabatic. VTST treatments which generally assume adiabatic dynamics, therefore, have a fundamental problem. Calculations of rate constants by VTST often exceed classical trajectory results by about 10 to 20percent. This is normally attributed to "recrossing trajectories”. In the present work it is shown, however, that deviations of this magnitude also have to be expected for nonadiabatic dynamics in comparison to adiabatic dynamics. It is, therefore, suggested that "recrossing” at least in part has to be attributed to nonadiabatic dynamics. A way out of the dilemma is the use of a combination of statistical adiabatic channel and classical trajectory concepts. © 2004 Oldenbourg Wissenschaftsverlag GmbH Thermodynamics & statistical physics nationallicence Laboratory techniques, experiments nationallicence Physical chemistry nationallicence Zeitschrift für Physikalische Chemie/International journal of research in physical chemistry and chemical physics Oldenbourg Wissenschaftsverlag GmbH 218/4/2004(2004-04-01), 457-468 0942-9352 218:4/2004<457 2004 218 zpch https://doi.org/10.1524/zpch.218.4.457.29195 text/html Onlinezugriff via DOI 1 research article jats NATIONALLICENCE 856 40 https://doi.org/10.1524/zpch.218.4.457.29195 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Troe Jürgen NATIONALLICENCE 773 0- Zeitschrift für Physikalische Chemie/International journal of research in physical chemistry and chemical physics Oldenbourg Wissenschaftsverlag GmbH 218/4/2004(2004-04-01), 457-468 0942-9352 218:4/2004<457 2004 218 zpch CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-gruyter